Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink filled chamber to expel a droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber near a discharge orifice. A plurality of chambers, each provided with a single heating element, are provided in the printer's printhead. The resistors are individually addressed with an energy pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. Preferably, each ink droplet travels along a substantially straight-line path as it moves from the orifice to the recording medium, such as paper. The straight-line path is generally perpendicular to the printhead. At times, a small amount of ink collects on the outer surface of the printhead around one or more of the orifices. As the droplets travel out of the orifices, they may be contacted by this excess ink causing them to be diverted from their intended straight-line paths of movement.
It would be desirable to provide an ink jet printer which generates droplets that travel along substantially straight-line paths even if ink collects around the printhead orifices and contacts the ejected droplets.